Method for impregnating a fibrous base material with a substantially air-free varnish

Abstract

A method and apparatus for impregnating a fibrous base material with a varnish liquid, wherein the so-impregnated base material is substantially air free. A base material is passed under the surface of and through a supply of low-viscosity liquid such as to impregnate the base material with the low-viscosity liquid and displace air from the base material so as to provide a substantially air-free base material. The air-free base material is passed through an entrance for and into a syphon. An inert gas is supplied to the syphon so as to maintain an inert gas atmosphere therein sufficient to maintain the air-free condition of the base material. The air-free base material is then passed through an exit of the syphon and under the surface of and through a supply of varnish liquid sufficiently to displace the low-viscosity liquid from the air-free base material and impregnate the air-free base material with the varnish liquid.

What is claimed is: 
     
       1. A method for impregnating a fibrous base material with a varnish liquid, wherein the so-impregnated base material is substantially air free, comprising: (a) passing the base material under the surface of and through a supply of low-viscosity liquid contained in a reservoir therefor such as to impregnate the base material with the low-viscosity liquid and displace air from the base material so as to provide a substantially air-free base material, said low viscosity liquid having a viscosity of about 100 cP or less;   (b) passing the air-free base material through an entrance for and into a syphon and pinching the base material at a first position near the syphon entrance but above the low-viscosity liquid surface, so as to remove from the base material a portion of the low-viscosity liquid therein and return the removed low-viscosity liquid portion to the supply thereof;   (c) supplying an inert gas which is soluble in the low-viscosity liquid into he syphon so as to maintain an inert gas atmosphere therein sufficient to maintain the air-free condition of the base material; and   (d) passing the air-free base material through an exit of the syphon and under the surface of and through a supply of varnish liquid contained in a reservoir therefor sufficiently to displace the low-viscosity liquid from the air-free base material and impregnate the air-free base material with the varnish, and pinching the base material at a second position near the syphon exit but above the varnish liquid surface, so as to prevent inert gas in the syphon from flowing into the varnish liquid, and pinching the base material between said first and second positions.   
     
     
       2. The method of claim 1 wherein the entrance of the syphon is beneath the surface of the low-viscosity liquid and the exit of the syphon is beneath the surface of the varnish liquid so as to provide a substantially air-tight syphon. 
     
     
       3. The method of claim 2 wherein a portion of the syphon is disposed above the surface of the low-viscosity liquid and a portion of the syphon is disposed above the surface of the varnish liquid such that a portion of the displaced low-viscosity liquid returns to the supply thereof. 
     
     
       4. The method of claim 1 wherein the low-viscosity liquid is soluble in the varnish liquid. 
     
     
       5. The method of claim 4 wherein the varnish liquid contains at least one varnish solvent and the low-viscosity liquid is the same as at least one of the varnish solvents. 
     
     
       6. The method of claim 1 wherein the temperature of the supply of low-viscosity liquid is greater than the temperature of the varnish liquid, so that inert gas dissolved in the low-viscosity liquid remaining in the base material entering the varnish liquid will not reboil.